1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) panel including a liquid crystal (LC) medium with positive dielectric anisotropy (Δ∈).
2. Discussion of the Background
There is a great demand for LCDs, in particular of the matrix type, which have very high specific resistance at the same time as a large working-temperature range, short response times even at low temperatures and low threshold voltage. LC media are required which facilitate the following advantages in LC cells:                extended nematic phase range (in particular down to low temperatures)        the ability to switch at extremely low temperatures (outdoor use, automobile, avionics)        increased resistance to UV radiation (longer service life).        
For LC cells, LC media are desired which enable greater multiplexability, lower threshold voltages and broader nematic phase ranges, in particular at low temperatures. A further widening of the available parameter latitude (clearing point, smectic-nematic transition or melting point, viscosity, dielectric parameters, elastic parameters) is also desired. Also, the LC media should have favourable values of ratio of the elastic constants K33/K11.
For TV, mobile and monitor applications, LC media are desired which have a fast response time and a low threshold voltage, furthermore a good LTS (low temperature stability). Also, depending on the thickness of the switchable LC layer, a moderate or high birefringence may be required. However, the LC media known in prior art have the disadvantage that they often do not allow all these requirements to be achieved simultaneously, without negatively affecting the other parameters of the LC cell.
Display mode of LC panels is determined in accordance with how to get LCs in an LC cell to align. TN (Twisted Nematic) mode, MVA (Multi-domain Vertical Alignment) mode, IPS (In-plane Switching) mode, OCB (Optically self-Compensated Birefringence) mode, and the like, are known as conventional LC panel display modes.
Among these, TN-LCD panels have been widely used, but have disadvantages such as slow response time and narrow viewing angle.
Further, an MVA mode (MVA-LCD) also has been known. In this mode, a pixel electrode in an active matrix substrate is provided with slits, and projections (ribs) for LC alignment control are formed on a counter electrode in a counter substrate, and the slits and the projections are used to form a fringe field, thereby aligning LC molecules in multiple different directions. In the MVA mode, each pixel region is divided into plural regions different in alignment direction of LC molecules, and thus multi-domain can be achieved per pixel region. Therefore, a widening of the viewing angle is allowed. Further, the MVA mode is one kind of VA mode, so that it provides contrast ratio (CR) higher than that of the respective TN, IPS, and OCB modes. However, the MVA mode still has room for improvements because it requires complicated production processes, and as in TN mode, has slow response time.
Recently, there has been proposed a TBA (Transverse Bend Alignment) mode where nematic LCs with positive dielectric anisotropy (Δ∈) (hereinafter, also referred to p-type nematic LCs) are used as an LC material, and the initial alignment of the LC molecules is vertical alignment, and comb-like electrodes are used to apply a voltage to the LC medium. In this mode, a pair of comb-like electrodes forms a transverse electric field, and under the influence of this electric field, the alignment behaviour of LC molecules is shown. The TBA mode is one kind of VA mode, so that it provides high contrast ratio. Further, the TBA mode requires no alignment control attributed to projections, and therefore, it has a simple pixel configuration and has excellent viewing angle characteristics.
As an example of the TBA mode, for example, Japanese Kokai Publication No. Hei-10-333171 discloses an LCD panel including: first and second substrates facing each other; a layer of LC materials that are injected between the first and second substrates and that are vertically aligned to the first and second substrates; and at least two electrodes parallel to each other formed in one of the first and second substrates.